PERIODIC COMETS. 



Enckc's Comet. It? Period arid Orbit. How its Motion shows the Existence of a resistii g Me- 

 dium. This Result corroborated by the Theory of Light. Newton's Conjectures resj ecting 

 Comet*. Bit-la's Comet. Its Period and Orbit. Lexell's Comet. Causes of its Appearance and 

 DisapiMjarance. Whiston's Comet. His Theory. Did this Comet produce the Deluge? Orbit 

 of this Comet. * 



